1. Field of the Invention
This invention relates to soft thermoplastic, segmented copolyester elastomers and to their use in pressure sensitive adhesives.
2. Description of the Prior Art
Segmented copolyester elastomers are not new. In U.S. Pat. No. 3,023,192 Shivers teaches segmented copolyesters containing about 25 to 65 percent by weight of short chain ester units preferably derived from an aliphatic glycol and an aromatic dicarboxylic acid, and about 35 to 75 percent by weight of long chain ester units preferably derived from a high molecular weight polyether glycol and an aromatic dicarboxylic acid which are useful for the preparation of spandex-type fibers.
In copending application Ser. No. 279,370, filed Aug. 10, 1972, now U.S. Patent 3,832,314, Hoh and Tsukamoto teach thermoplastic compositions containing (A) 1 to 99 percent by weight of thermoplastic segmented copolyester elastomer consisting essentially of a multiplicity of recurring short chain ester units and long chain ester units joined through ester linkages, said short chain ester units amounting to 15 to 75 percent by weight of said copolyester and being of the formula ##EQU1## and said long chain ester units amounting to 25 to 85 percent by weight of said copolyester and being of the formula ##EQU2## wherein R is the divalent aromatic radical remaining after removal of the carboxyl groups from aromatic dicarboxylic acid having a molecular weight of less than 350, D is the divalent radical remaining after removal of the hydroxyl groups from organic diol having a molecular weight of less than 250, and G is the divalent radical remaining after removal of the terminal hydroxyl groups from long chain glycol having an average molecular weight of 350 to 6000, said copolyester having a melt index of less than 150 and a melting point of at least 125.degree.C., and (B) 1 to 99 percent by weight of low molecular weight thermoplastic resin which forms compatible mixtures with the segmented copolyester, is thermally stable at 150.degree.C., and has a melt viscosity of less than 10,000 centipoises at 200.degree.C.
Although the compositions of the Hoh and Tsukamoto patent have good bond strength as hot melt adhesives, they do not make particularly good pressure sensitive adhesives. In order to provide good pressure sensitive adhesive properties, it is necessary that the adhesive remain tacky on its surface for an extended period of time. The pressure sensitive adhesive compositions exemplified in the Hoh and Tsukamoto patent had to be used immediately because they lacked this quality.